Control system for the electric fuel pump of an internal combustion engine

ABSTRACT

A control system is described for the electric fuel pump of an internal combustion engine, with a sensor for the speed of a shaft of the engine and with a logic circuit for providing a shut off signal for the pump, depending on the speed detected, where the signal of a further sensor (14) for the speed is supplied to the a logic circuit (16, 17), and where shut off then takes place only when both speed signals deviate from a specified range. In this way, it is ensured that the vehicle remains drivable if one of the two sensors (13) or (14) fails.

BACKGROUND OF THE INVENTION

The invention is based on a control system for the electric fuel pump ofan internal combustion engine From DE-PS 1 526 504, a circuitarrangement for driving a fuel pump in an internal combustion engine isknown, in which below a minimum engine speed, the supply of electricityto the fuel pump is cut off. The circuit arrangement described there isbased on the concept that, when the ignition is switched on, the enginespeed drops below minimum values only when the engine is braked byexternal intervention, especially in the case of an accident. In thiscase, for reasons of safety, the supply of fuel from the tank in thedirection towards the engine should be interrupted. Furthermore, in theGerman Published Patent Applications 20 65 928 and 22 49 235, devicesare described which, for the same aforementioned reasons, interrupt thesupply of fuel to the engine when it is stopped. There, this standstillof the engine is detected via an appropriate detection of the air flowin the induction manifold, in that in the idle position of the air flowmeter flaps in the intake pipe, a switch is activated accordingly, andthat depending on this switch activation, the electricity supply to theelectrically driven fuel pump is then also interrupted. Naturally, forthe case of start-up, suitable measures must be taken, in order todeactivate this safety function, especially at the beginning ofstart-up.

It has now been shown that with the conventional safety cut-out of theelectrical fuel pump in internal combustion engines, possibilities oferrors can arise which lead to unwarranted triggering of this safetycut-out.

SUMMARY OF THE INVENTION

It is therefore the object of this invention to develop and provide asafe and reliable control system for an electrical fuel pump of aninternal engine having an improved safety shut off.

According to the invention, the control system for an electricallydriven fuel pump of an internal combustion engine comprises means forsensing a speed of a shaft of the engine, means for sensing anotherspeed, and logic means for generating a shut off signal for the fuelpump. The logic means is connected to both sensing means and hascomparison means receiving speed signals from said sensing means forshutting off the fuel pump only if both speeds deviate from a specifiedspeed range.

With the control system for the electric fuel pump of an internalcombustion engine in accordance with the invention, a high degree ofsafety and reliability of a fuel pump shut off system is achieved, whichcan, moreover, be realised in a simple manner.

BRIEF DESCRIPTION OF THE DRAWING

The objects, features and advantages of the present invention will nowbe illustrated in more detail by the following detailed description,reference being made to the accompanying drawing in which:

The sole FIGURE is a block diagram of a device for controlling anelectric fuel pump of an internal combustion engine according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The embodiment shown in the drawing is a control system for the electricfuel pump of an internal combustion engine, in which the electric motorof the fuel pump, not shown in further detail, is designated 10. Itreceives its supply voltage E_(Batt) via a switch 11 from a supply line12.

13 represents a first sensor for a first engine speed; 14 is a secondsensor for a second engine speed. In the concrete case, the sensor 13 isassigned to the engine crankshaft, and the sensor 14 to the camshaft. Onthe output side, the two sensors 13 and 14 are connected to a block 15,in which one threshold value interrogation each, 16a and 16b, issymbolically shown for the signals of the two sensors 13 and 14, as isan AND-gate 17 for the output signals of the threshold valueinterrogations. For its part, this AND-gate 17 in turn controls theswitch 11 between the electricity supply line 12 and the electric motor10 of the fuel pump. To complete it, block 15 is connected with theelectricity supply line 12 via a supply voltage connection 19.

The fundamental idea of the present invention is that the switch 11,connected in series with the electric motor 10 of the fuel pump, opens,depending on the engine speed, only when both the signal from sensor 13and the signal from sensor 14 show a minimum value. In this way it isensured that the vehicle can still be driven if one of the two sensors13 or 14 should fail.

The AND-gate 17, shown in block 15, in conjunction with the pre-receivedthreshold value interrogations, carry out a generally known plausibilityinterrogation of the two signals from the sensors 13 and 14, and onlywhen these two signals are plausible relative to each other, and bothspeed values fall below a selectable lower value, is the switch 11opened.

It has proved to be particularly expedient if the two sensors 13 and 14are assigned to different shafts of the internal combustion engine, i.e.sensor 13, for example, to the crankshaft, and sensor 14 to thecamshaft. Naturally the plausibility interrogation of the output signalsof the sensors 13 and 14 must take into account the differing absolutevalues, or the relationship, between crankshaft speed and camshaftspeed.

It is of course necessary to ensure that at the beginning of a start-upprocess, the fuel pump can actually supply fuel. To this end, means areenvisaged which render the plausibility interrogation ineffective duringthe phases of the start-up process.

In addition to switching off the fuel pump at low engine speed, thecontrol system in accordance with this invention can also be employed asan overspeed protection for the engine, in that the electricity supplyto the fuel pump is then interrupted if critical safety speeds areexceeded. In this case too, the system can activate if the plausibilityinterrogation of both values of the sensors 13 and 14 show that acritical safety speed is exceeded.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in acontrol system for the electric fuel pump of an internal combustionengine, it is not intended to be limited to the details shown, sincevarious modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.
 1. Control system for an electricallydriven fuel pump of an internal combustion engine, said control systemcomprising first means for sensing a speed of a shaft of said engine,second means for sensing another speed, and logic means for generating ashut off signal for said fuel pump, said logic means being connected toboth of said sensing means and having comparison means for generatingsaid shut off signal so as to shut off said fuel pump only if both ofsaid speeds sensed by both said first and second means deviate from apredetermined speed range but not to shut off said fuel pump if only oneof said speeds sensed by only one of said means deviates from apredetermined speed range.
 2. Control system as defined in claim 1,wherein said internal combustion engine has a crankshaft and a camshaft,and said first means for sensing a speed of a shaft of said enginedetects a crankshaft speed of said engine and said second means forsensing another speed detects a camshaft speed of said engine. 3.Control system as defined in claim 1, wherein said logic means includesswitching means for interrupting a flow of electricity to saidelectrically driven fuel pump if both of said speeds sensed by both saidfirst and second means deviate from said predetermined speed range, andwherein said predetermined speed range is defined by a minimum andmaximum speed value.
 4. Control system as defined in claim 1, furthercomprising means for preventing said logic means from shutting off saidfuel pump when said internal combustion engine is being started.